Physical parameters such as temperature and pressure can be converted into electrical signals by a device known as a transducer. Transducers are found in gauges or sensors for measuring these physical parameters, such as quartz gauges or strain gauges. A quartz gauge, for example, includes a crystal that changes resonant frequency in response to an applied mechanical stress. This stress may be induced by pressure, temperature, and often a combination of both. Other gauges include materials that react to outside stimuli resulting in a measurable electrical response.
It is these reactive materials, whether it is a quartz crystal or a metallic member, that are susceptible to pressure and temperature fluctuations in a surrounding environment. Quartz gauges, for example, that are used in subterranean wells are particularly subject to pressure errors caused by static and dynamic temperatures. Particularly complex, rugged, and caustic is the downhole drilling environment, creating temperature and pressure transient conditions which often distort the measurements taken by precision gauges. There is a strong correlation between accurate downhole measurements and thermal stability of the measurement device. However, compensating for temperature gradients produced by either external heating or by pressure-volume heating has proven difficult.
High precision gauges used in downhole environments require long times to stabilize with their surroundings, which are much different than those at the surface of a well. To obtain accurate data from high precision gauges, the tool assembly having the gauge is held at a depth in the well and the gauge is allowed to come to thermal equilibrium with its surroundings. Whether the time to equilibrium is minutes or hours, the time is very valuable in the cost-sensitive process of well operations. Often, the gauges are fitted with a large contact member or surfaces that communicate with the well bore in an effort to hasten thermal equilibrium. However, downhole tool assemblies often involve packaging components in close proximity to each other, therefore restricting the amount of usable space for such components.
The design of pressure transducers has long been an effort to minimize temperature effects, or to accurately determine the temperature and correct the pressure reading through modeling and signal processing. The combination of quickly obtaining accurate measurements from precision gauges in an unstable downhole environment and compact tool assembly designs is pushing the limits of current downhole precision gauges.